Introduction: Hypothermia (HT) applied after HI has shown neuroprotecton after 1 week of survival in both adult and neonatal animal models. In adult models post-HI hypothermic protection have been inconsistent after longer survival.Our randomised study of post-HI HT examined pathology and functional ability in neonatal rats of both sexes after 1 or 6weeks.Methods: On postnatal day seven (P7) 106 rat pups of both sexes had their left carotid artery ligated, followed by 70 min hypoxia (n=94)(7.70% O2 in N2) at 36°C Tair (Trectal≈37°C). The pups were then randomized to 6h HT (target Trectal 32°C) or normothermia (NT) (Trectal 37°C) in separate chambers before returning to the dam for 1(n=32) or 6(n=62) weeks survival. Brain sections were stained with H&E and examined for morphological changes in cortex, hippocampus, basal ganglia (BG) and thalamus on a 9 step scale at five coronal levels. At P42 and P49 61 animals and 20 controls (CT) were sensorimotor tested with postural reflex/ limb placing, foot-fault, swing and paw-preference test with results pooled as a functional total rank for each animal. Results: At one week survival HT reduced the neuropathological damage in both male and female rats by 25% (thalamus), 27% (cortex), 28% (BG) and 43% (hippocampus) as compared to NT. After 6 weeks survival a significant reduction of the brain lesion of HT vs NT animals was seen only in the female HT rats by 57% (thalamus), 40%(cortex), 59% (BG) and 54% (hippocampus) as compared to female NT rats. Total functional rank correlated well with neuropathological outcome in female(r=0.77) rats an differed between NT (100±34) and HT(150±35)rats. Conclusion: Posthypoxic HT is neuroprotective in neonatal rats of both sexes after 1 weeks survival. After 6 weeks only female rats show protection from HT, possibly due to hormonal influence on neuronal injury.